Interpretive Summary: Pesticides are used by farmers and landowners to control weeds, insects, and plant diseases. A portion of the pesticide may be transported by rainfall through the soil and eventually migrate to groundwater sources. The sandy, Coastal Plain region of North Carolina may be susceptible to pesticide leaching due to the high pesticide usage; sandy, low organic matter soils; high rainfall; and shallow water tables. Because a high proportion of the general public in this region relies heavily on groundwater as a drinking water source, the USDA initiated a study in a watershed (Herrings Marsh Run, Duplin Co., NC) to determine if pesticides were present. The HMR watershed is typical of other watersheds in the region and has some intensive animal and agricultural production. Groundwater samples were collected from 92 wells on 21 farms from 1993 to 1996 and were sampled for 11 commonly used pesticides by farmers and landowners within the watershed. No pesticides were detected in 88 of the 92 wells tested over the three-year period. Pesticides were detected in four wells, but the concentrations were usually below the health advisory level. The high number of wells (95%) without pesticide detections suggests that pesticides had a minimal impact on the quality of HMR groundwater.

Technical Abstract:
Pesticide and metabolite detection in drinking water sources is of concern because of potential health risks due to consumption of water containing these compounds. A 3-yr study was conducted to assess the presence of pesticides and metabolites in shallow groundwater of a USDA Water Quality Demonstration Project. Ninety-two shallow groundwater monitoring wells were installed in and around the Herrings Marsh Run (HMR) watershed located in the Coastal Plain region of southeastern North Carolina. Water samples were collected monthly from March 1993 to March 1995 and collected quarterly for the remainder of 1995 and early 1996. Samples were initially screened for triazine and chloroacetamide herbicides using immunoassay techniques, and positive detections were further analyzed for additional pesticides using gas chromatographic (GC) and GC/MS (mass spectrometric) procedures. During the study period, GC and GC/MS results revealed that the majority (95%) of the wells had no detections for 11 pesticides commonly used in the watershed. Pesticides were consistently detected in four wells, but the concentrations were usually below the health advisory limit. Among the four wells, alachlor was the most frequently detected pesticide. The high number of wells without pesticide detections suggests that pesticides have had a minimal impact on the quality of HMR shallow groundwater.